Node REPL does not honor `uncaughtException` listeners

[AyushG3112]

• Version: master
• Platform: Linux blocky 4.13.0-38-generic The binary and long term compatibility with node #43~16.04.1-Ubuntu SMP Wed Mar 14 17:48:43 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

REPL commands

$ node
> process.on('uncaughtException', (err) => console.log('caught' + err));
> throw 'hi';

OUTPUT :

Thrown: hi

Running process.hasUncaughtExceptionCaptureCallback() in the REPL console outputs true, so it is understandable why the listener isn't called.

However

> process.setUncaughtExceptionCaptureCallback(null);

throws the Error:

Error [ERR_DOMAIN_CANNOT_SET_UNCAUGHT_EXCEPTION_CAPTURE]: The `domain` module is in use, which is mutually exclusive with calling process.setUncaughtExceptionCaptureCallback()
    at process.setUncaughtExceptionCaptureCallback (domain.js:97:15)
    at repl:1:9
    at Script.runInThisContext (vm.js:91:20)
    at REPLServer.defaultEval (repl.js:311:29)
    at bound (domain.js:396:14)
    at REPLServer.runBound [as eval] (domain.js:409:12)
    at REPLServer.onLine (repl.js:609:10)
    at REPLServer.emit (events.js:187:15)
    at REPLServer.emit (domain.js:442:20)
    at REPLServer.Interface._onLine (readline.js:285:10)
----------------------------------------
Error: require(`domain`) at this point
    at domain.js:93:28
    at NativeModule.compile (internal/bootstrap/loaders.js:209:7)
    at NativeModule.require (internal/bootstrap/loaders.js:137:18)
    at repl.js:63:16
    at NativeModule.compile (internal/bootstrap/loaders.js:209:7)
    at NativeModule.require (internal/bootstrap/loaders.js:137:18)
    at internal/repl.js:4:14
    at NativeModule.compile (internal/bootstrap/loaders.js:209:7)
    at Function.NativeModule.require (internal/bootstrap/loaders.js:137:18)
    at startup (internal/bootstrap/node.js:240:40)

I could not find any documentation of this behaviour for the Node REPL.

Is this a bug, or is this a desired behaviour which has to be documented?

[addaleax]

This is happening because the repl uses the domain module to do its own error handling, so I don’t really think it’s a bug.

We could maybe be a bit more forward and explicitly disable process.on('uncaughtException') in the REPL?

[AyushG3112]

@addaleax That's what I thought to, but instead of disabling process.on('uncaughtException'), can't we remove the default error handling from domain module if any uncaughtException listeners exist, with a message to the user?

In either case, we do need to document this.

[AyushG3112]

I'll open a PR this Monday to document this behaviour, unless someone beats me to it or we decide to change something.

[AyushG3112]

@addaleax before I start on documenting this, 1 question: what're your thoughts on replacing the error handling via domain with a default process.on('uncaughtException') listener?

[addaleax]

@AyushG3112 My thoughts are that that’s probably very hard to get that to work, because in general there can be multiple REPL instances in a process, which need to keep track of async context in order to determine whether they should handle an exception